Dispersions containing pyrogenic oxides

ABSTRACT

Dispersions of pyrogenic oxides, doped using an aerosol, are prepared by mixing the oxide with a suspending agent and milling. The dispersions can be used to prepare inkjet paper.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to Europen application00107817.9 filed on Apr. 12, 2000, the subject matter of which is herebyincorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention is directed to dispersions, a process forpreparing these dispersions and their use in the preparation of coatingmixtures for inkjet media.

BACKGROUND OF THE INVENTION

[0003] It is known that dispersions, for example water-baseddispersions, can be prepared from pyrogenically prepared oxides. Aqueousdispersions can be used to prepare coating mixtures which are applied topaper or films. The coated films may then be printed using an inkjetprinter. In this case, one objective is to obtain dispersions which arefilled as highly as possible (high solids content) but with a lowviscosity.

SUMMARY OF THE INVENTION

[0004] The invention provides dispersions which are characterised inthat they consist of a liquid phase, preferably water, and a solidphase. The solid phase consists of a pyrogenic oxide, doped using anaerosol, the BET surface area of which is between 5 and 600 m²/g. Thepyrogenic oxide preferably comprises silica prepared by the method offlame hydrolysis or flame oxidation and which has been doped with one ormore doping component(s). Preferably the doping component is analuminium oxide, and doping is accomplished by the method of aerosolapplication, in which the amount of doped material is between 1 and200,000 ppm and the doping component(s) are applied via a salt or a saltmixture. The solid phase in the dispersion should be present in aproportion by weight between 0.001 and 80 wt. %.

[0005] The invention also provides a process for preparing chemicaldispersions in which a pyrogenic oxide, doped using an aerosol, isintroduced into a liquid, preferably water, in a proportion by weight ofbetween 0.001 and 80 wt. %. This dispersion is then that patent, 85 kg/hof SiCl₄ are evaporated, mixed with 51 Nm³/h of hydrogen and with 70Nm³/h of a nitrogen/oxygen mixture (containing 35 vol. % O₂, remainderN₂) and fed into the central tube in the burner. The gas mixture flowsout of a nozzle and bums in a water-cooled combustion chamber. 4 Nm³/hof (jacket) hydrogen flows out of the jacket nozzle which surrounds thecentral nozzle, in order to avoid incrustations. 70 Nm³/h of secondaryair are also introduced into the combustion chamber.

[0006] An aerosol flows into the central tube out of an axial tubelocated therein. The aerosol is produced by atomising a 15% aqueousAlCl₃ solution using a two-fluid nozzle. An aerosol flow of 1 kg/h(aqueous salt solution) is produced in which a carrier gas stream of 16Nm³/h of air conveys the aerosol through a heating section. Theair/aerosol gas mixture then enters the central tube from the axial tubeat about 180° C. The aerosol is burned together with the air/SiCl₄mixture. The reaction gases and the pyrogenically prepared silica dopedwith aluminium oxide are removed under suction through a cooling system,and cooled by applying a reduced pressure. The solid material (dopedpyrogenic oxide) is separated from the gas stream in a filter or acyclone.

[0007] The doped pyrogenically prepared silica is produced as a white,finely divided powder. Adhering residues of hydrochloric acid areremoved by treatment at elevated temperature with air which containswater vapour. The pyrogenic silicon dioxide doped using an aerosol hasthe following physico-chemical characteristics: BET: 60 m²/g pH (4% aqu.disp.): 3.9 Compacted bulk density: 142 g/l Chloride content: 180 ppmAl₂O₃ content 0.19 wt. % DBP absorption: 73 g/100 g

[0008] An aqueous dispersion is prepared with the doped pyrogenic oxide.A commercially available Aerosils (pyrogenically prepared silica)provided by Degussa-Hüls AG/Frankfurt, OX 50 and Aerosil 90, are used ascomparison examples.

[0009] Table 1 gives the characteristics of the oxides: TABLE 1Physico-chemical characteristics of the doped pyrogenic oxide Dopedpyrogenic oxide according to example OX 50 Aerosil 90 BET m²/g 60 50 90pH (4% aqu. disp.) 3.9 3.8-4.8 3.7-4.7 Compacted bulk density 142 130 80g/l Chloride content 180 <250 <250 ppm Al₂O₃ content wt. % 0.19 <0.080.05 SiO₂ content wt. % 99.8 >99.8 >99.8

[0010] An aqueous dispersion is prepared using these three differentpyrogenic oxides. This is achieved using a rotor-stator system(Ultra-Turrax™) with a dispersion time of 30 minutes in a double-walledvessel with water cooling. It is attempted to prepare a 40% (withrespect to solids) dispersion (w=0.40). This dispersion may also beprepared using other equipment, e.g., ball mills or pearl mills orvarious types of jet or high-pressure mills (jets of liquid directedtowards each other). It is shown that it is not possible to produce a40% dispersion with Aerosil 90 using this system because the system istoo highly viscous. The viscosity of the dispersions prepared in thisway (doped oxide and Aerosil OX 50) is measured after 2 h with aBrookfield viscometer. TABLE 2 Viscosity of the 40% aqueous dispersionDoped pyrogenic Aerosil 90: oxide according not possible to prepare a40% to example 1 OX 50 dispersion using Ultra-Turrax 5 rpm 24202320 >10,000 l0 rpm 1520 1320 20 rpm 970 745 50 rpm 554 372 100 rpm 370256

[0011] Inkjet coating mixtures are prepared from these 40% aqueousdispersions. Formulation for preparing an inkjet coating mixture is asfollows. Two dispersions, A and B, are prepared. Dispersion A is a 40%(w=0.40 ) aqueous dispersion which contains the pyrogenic oxide (or thedoped pyrogenic oxide). This is made by dispersing the pyrogenic oxideor doped oxide for 30 minutes with an Ultra-Turrax system in awater-cooled double-jacket system.

[0012] Dispersion B is a 10% (with respect to PVA) aqueous dispersion ofpolyvinyl alcohol (solid, abbreviated as PVA), Mowiol 26-88 from theClariant Co. The two dispersions A and B are combined over the course of10 minutes by stirring at 500 rpm with a dissolver disc to give adispersion C. Dispersions A and B are mixed in such a way that a ratioby weight of Aerosil (or doped pyrogenic oxide) to PVA of 100:20 isproduced in subsequent dispersion C. In the case of a 40% dispersion A,this is mixed with dispersion B in the ratio by weight of 1.25:1 inorder to achieve the required ratio by weight (100:20 for the solids).Furthermore (if required) enough water is added to produce a 24%dispersion C, with respect to the sum of the solids (progenic oxide+PVA). The viscosity of this dispersion C, the inkjet coating mixture, ismeasured after 24 h using a Brookfield viscometer. TABLE 3 Viscosity ofthe coating mixture measured after 24 h Doped oxide according to example1 OX 50 Aerosil 90 Solids content of the 24 24 22.5 coating mixture(pyrogenic oxide + PVA) wt. % Viscosity [mPas] 3244 685 3352 at 100 rpm

[0013] (Note: In the case of preparing the coating mixture from Aerosil90, a 30% aqueous dispersion is used initially.)

[0014] These coating mixtures are applied to an untreated polyester film(thickness 100 micrometers) with the aid of a shaped spreading rod. Thewet film thickness of the coating mixture is 120 micrometers. Thecoating is dried at 105° C. for 8 minutes. The also very good. Althoughdispersions made with Aerosil OX 50 also have a relatively lowviscosity, the print quality of the coating mixtures, or coatings,prepared therefrom is not acceptable.

What is claimed is:
 1. A dispersion comprising a liquid phase and asolid phase, wherein the solid phase comprises a pyrogenic oxide, andwherein said pyrogenic oxide: a) is doped with one or more dopingcomponents; and b) has a BET surface area of between 5 and 600 m²/g. 2.The dispersion of claim 1 , wherein said pyrogenic oxide is silica. 3.The dispersion of claim 1 , wherein said liquid phase is water.
 4. Thedispersion of any one of claims 1-3, wherein said pyrogenic oxide isprepared by the method of flame hydrolysis or flame oxidation.
 5. Thedispersion of any one of claims 1-3, wherein said pyrogenic oxide isdoped using an aerosol.
 6. The dispersion of any one of claims 1-3,wherein said pyrogenic oxide is doped with aluminum oxide.
 7. Thedispersion of any one of claims 1-3, wherein the amount of dopedmaterial in said pyrogenic oxide is between 1 and 200,000 ppm.
 8. Thedispersion of claim 6 , wherein the amount of doped material in saidpyrogenic oxide is between 1 and 200,000 ppm.
 9. The dispersion of claim8 , wherein said doped material is applied as a salt or a salt mixture.10. The dispersion of any one of claims 1-3, wherein the solid phase inthe dispersion is present in a proportion by weight of between 0.001 and80 wt. %.
 11. The dispersion of claim 6 , wherein the solid phase in thedispersion is present in a proportion by weight of between 0.001 and 80wt. %.
 12. A process for preparing a dispersion according to claim 1 ,comprising: a) mixing a doped pyrogenic oxide with a liquid; and b)milling the mixture produced in step a).
 13. The process of claim 12 ,wherein said liquid is water and said pyrogenic oxide is silica.
 14. Theprocess of claim 12 , wherein said pyrogenic oxide is present in saidliquid in a proportion by weight of between 0.001 and 80 wt. %.
 15. Theprocess of claim 12 , wherein said milling procedure is performed usingan ball mill.
 16. The process of claim 12 , wherein said millingprocedure is performed using a pearl mill.
 17. The process of claim 12 ,wherein said milling procedure is performed using a high pressuremilling mixture.
 18. A coating mixture for an inkjet paper or inkjetfilm comprising the dispersion of claim 1 .